CDKN2A-p16 Deletion and Activated KRASG12D Drive Barrett's-Like Gland Hyperplasia-Metaplasia and Synergize in the Development of Dysplasia Precancer Lesions

BACKGROUND & AIMS

Barrett's esophagus is the precursor of esophageal dysplasia and esophageal adenocarcinoma. CDKN2A-p16 deletions were reported in 34%-74% of patients with Barrett's esophagus who progressed to dysplasia and esophageal adenocarcinoma, suggesting that p16 loss may drive neoplastic progression. KRAS activation frequently occurs in esophageal adenocarcinoma and precancer lesions. LGR5+ stem cells in the squamocolumnar-junction (SCJ) of mouse stomach contribute as Barrett's esophagus progenitors. We aimed to determine the functional effects of p16 loss and KRAS activation in Barrett's-like metaplasia and dysplasia development.

METHODS

We established mouse models with conditional knockout of CDKN2A-p16 (p16KO) and/or activated KRASG12D expression targeting SCJ LGR5+ cells in interleukin 1b transgenic mice and characterized histologic alterations (mucous-gland hyperplasia/metaplasia, inflammation, and dysplasia) in mouse SCJ. Gene expression was determined by microarray, RNA sequencing, and immunohistochemistry of SCJ tissues and cultured 3-dimensional organoids.

RESULTS

p16KO mice exhibited increased mucous-gland hyperplasia/metaplasia versus control mice (P = .0051). Combined p16KO+KRASG12D resulted in more frequent dysplasia and higher dysplasia scores (P = .0036), with 82% of p16KO+KRASG12D mice developing high-grade dysplasia. SCJ transcriptome analysis showed several activated pathways in p16KO versus control mice (apoptosis, tumor necrosis factor-α/nuclear factor-kB, proteasome degradation, p53 signaling, MAPK, KRAS, and G1-to-S transition).

CONCLUSIONS

p16 deletion in LGR5+ cell precursors triggers increased SCJ mucous-gland hyperplasia/metaplasia. KRASG12D synergizes with p16 deletion resulting in higher grades of SCJ glandular dysplasia, mimicking Barrett's high-grade dysplasia. These genetically modified mouse models establish a functional role of p16 and activated KRAS in the progression of Barrett's-like lesions to dysplasia in mice, representing an in vivo model of esophageal adenocarcinoma precancer. Derived 3-dimensional organoid models further provide in vitro modeling opportunities of esophageal precancer stages.

Abstract 929: CDKN2A/p16 knockout in LGR5+ progenitor cells augments mucous gland hyperplasia/metaplasia, inflammation, and dysplasia in mouse stomach squamocolumnar junction

Background: Esophageal adenocarcinoma (EAC) develops in pre-cancer columno-glandular hyperplasia, intestinal metaplasia and dysplasia that replaces squamous epithelium and characterizes Barrett’s esophagus (BE). We reported CDKN2A/p16 deletions in up to 69% of BE patients who progressed to dysplasia and EAC, suggesting that p16 loss may drive progression of BE to EAC. LGR5+ cardia like stem cells in the squamocolumnar junction (SCJ) of mouse stomach have been implicated in the cellular origins of BE, and glandular hyperplasia/metaplasia (MGHP) and dysplasia and enhanced inflammation in SCJ were reported in interleukin 1 beta (IL1b) transgenic mice. Our hypothesis is that p16 deletion in LGR5+ cells that give rise to glandular epithelium in SCJ of IL1b mice may accelerate glandular hyperplasia and metaplasia and augment progression to dysplasia and EAC.

Design: We tested the hypothesis using conditional knockout of CDKN2A/p16 in IL1b mouse targeting SCJ LGR5+ cells. Model A genotype is p16del: (Lgr5-CreERT2 +/-; IL1b wt/tg; p16 fl/fl) and control model C is p16 wild type (wt): (Lgr5-CreERT2 +/-; IL1b wt/tg; p16 wt/wt). Conditional knockout was induced with intraperitoneal tamoxifen injection. All mice were given bile acid in drinking water, daily. Mice were euthanized and gross and histologic alterations in SCJ, stomach, small intestine (SI) and colon were assessed over time, until 16 months. MGHP was scored as the number of glandular profiles in each section of SCJ, and inflammation and dysplasia were evaluated and scored (0 to 3) in H&E-stained sections.

Results: We examined 39 mice: 19 model A (p16del) and 20 model C (p16wt). Mice were grouped into 3 groups from 3 to 16 months. The SCJ of p16del mice exhibited larger areas of hyperplastic cardia-type mucous glands compared to p16wt mice, showing higher numbers of gland profiles (median 17 vs. 8 gland profiles, P=9-5). Higher inflammation scores were also seen in p16del mice ages 3-7 and 7-12 months (P=.036 and P=.013). P16del mice showed higher dysplasia scores overall (P=.013), particularly in mice ages 7-16 months (P=.038). There was a positive correlation between MGHP and inflammation (P=.004) and between inflammation and dysplasia (P=.021). No significant alterations were seen in the stomach, SI, or colon of p16del vs p16wt mice.

Conclusions: Loss of p16 alone is not sufficient to develop neoplastic alterations in stomach, SI and colon. Deletion of p16 in LGR5+ cardia-like stem cells in the squamocolumnar junction of mouse stomach, together with IL1b and BA-induced inflammation and cellular injury, is associated with increased MGHP, inflammation, and dysplasia. The model implicates p16 in the early stages of esophageal carcinogenesis, similar to human disease, providing a model to further dissect the contributing molecular mechanisms of progression to esophageal dysplasia and cancer.

Citation Format: Jing Sun, Elena V. Komissarova, Caitlin Hills, Tyler Seckar, Gloria H. Su, Jorge Sepulveda, Timothy L. Wang, Antonia R. Sepulveda. CDKN2A/p16 knockout in LGR5+ progenitor cells augments mucous gland hyperplasia/metaplasia, inflammation, and dysplasia in mouse stomach squamocolumnar junction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 929.

The number of titrated microRNA species dictates ceRNA regulation

microRNAs (miRNAs) play key roles in cancer, but their propensity to couple their targets as competing endogenous RNAs (ceRNAs) has only recently emerged. Multiple models have studied ceRNA regulation, but these models did not account for the effects of co-regulation by miRNAs with many targets. We modeled ceRNA and simulated its effects using established parameters for miRNA/mRNA interaction kinetics while accounting for co-regulation by multiple miRNAs with many targets. Our simulations suggested that co-regulation by many miRNA species is more likely to produce physiologically relevant context-independent couplings. To test this, we studied the overlap of inferred ceRNA networks from four tumor contexts-our proposed pan-cancer ceRNA interactome (PCI). PCI was composed of interactions between genes that were co-regulated by nearly three-times as many miRNAs as other inferred ceRNA interactions. Evidence from expression-profiling datasets suggested that PCI interactions are predictive of gene expression in 12 independent tumor- and non-tumor contexts. Biochemical assays confirmed ceRNA couplings for two PCI subnetworks, including oncogenes CCND1, HIF1A and HMGA2, and tumor suppressors PTEN, RB1 and TP53. Our results suggest that PCI is enriched for context-independent interactions that are coupled by many miRNA species and are more likely to be context independent.

Downregulation of Friend Leukemia Integration 1 (FLI1) follows the stepwise progression to gastric adenocarcinoma

Gastric adenocarcinoma (GC) is a leading cause of cancer-related deaths worldwide. The transcription factor gene Friend Leukemia Integration 1 (FLI1) is methylated and downregulated in human GC tissues. Using human GC samples, we determined which cells downregulate FLI1, when FLI1 downregulation occurs, if FLI1 downregulation correlates with clinical-pathologic characteristics, and whether FLI1 plays a role in invasion and/or proliferation of cultured cells. We analyzed stomach tissues from 98 patients [8 normal mucosa, 8 intestinal metaplasia (IM), 7 dysplasia, 91 GC] by immunohistochemistry for FLI1. Epithelial cells from normal, IM, and low-grade dysplasia (LGD) showed strong nuclear FLI1 staining. GC epithelial cells showed significantly less nuclear FLI1 staining as compared to normal epithelium, IM and LGD (P=1.2×10^-5, P=1.4×10^-6 and P=0.006, respectively). FLI1 expression did not correlate with tumor stage or differentiation, but was associated with patient survival, depending on tumor differentiation. We tested the functional role of FLI1 by assaying proliferation and invasion in cultured GC cells. Lentiviral-transduced FLI1 overexpression in GC AGS cells inhibited invasion by 73.5% (P = 0.001) and proliferation by 31.5% (P = 0.002), as compared to controls. Our results support a combined role for FLI1 as a suppressor of invasiveness and proliferation in gastric adenocarcinoma, specifically in the transition from pre-cancer lesions and dysplasia to invasive adenocarcinoma, and suggest that FLI1 may be a prognostic biomarker of survival in gastric cancers.

High-resolution genomic alterations in Barrett's metaplasia of patients who progress to esophageal dysplasia and adenocarcinoma

The main risk factor for esophageal dysplasia and adenocarcinoma (DAC) is Barrett's esophagus (BE), characterized by intestinal metaplasia. The critical genomic mechanisms that lead to progression of nondysplastic BE to DAC remain poorly understood and require analyses of longitudinal patient cohorts and high-resolution assays. We tested BE tissues from 74 patients, including 42 nonprogressors from two separate groups of 21 patients each and 32 progressors (16 in a longitudinal cohort before DAC/preprogression-BE and 16 with temporally concurrent but spatially separate DAC/concurrent-BE). We interrogated genome-wide somatic copy number alterations (SCNAs) at the exon level with high-resolution SNP arrays in DNA from formalin-fixed samples histologically confirmed as nondysplastic BE. The most frequent abnormalities were SCNAs involving FHIT exon 5, CDKN2A/B or both in 88% longitudinal BE progressors to DAC vs. 24% in both nonprogressor groups (p = 0.0004). Deletions in other genomic regions were found in 56% of preprogression-BE but only in one nonprogressor-BE (p = 0.0004). SCNAs involving FHIT exon 5 and CDKN2A/B were also frequently detected in BE temporally concurrent with DAC. TP53 losses were detected in concurrent-BE but not earlier in preprogression-BE tissues of patients who developed DAC. CDKN2A/p16 immunohistochemistry showed significant loss of expression in BE of progressors vs. nonprogressors, supporting the genomic data. Our data suggest a role for CDKN2A/B and FHIT in early progression of BE to dysplasia and adenocarcinoma that warrants future mechanistic research. Alterations in CDKN2A/B and FHIT by high-resolution assays may serve as biomarkers of increased risk of progression to DAC when detected in BE tissues.

A precision oncology approach to the pharmacological targeting of mechanistic dependencies in neuroendocrine tumors

We introduce and validate a new precision oncology framework for the systematic prioritization of drugs targeting mechanistic tumor dependencies in individual patients. Compounds are prioritized on the basis of their ability to invert the concerted activity of master regulator proteins that mechanistically regulate tumor cell state, as assessed from systematic drug perturbation assays. We validated the approach on a cohort of 212 gastroenteropancreatic neuroendocrine tumors (GEP-NETs), a rare malignancy originating in the pancreas and gastrointestinal tract. The analysis identified several master regulator proteins, including key regulators of neuroendocrine lineage progenitor state and immunoevasion, whose role as critical tumor dependencies was experimentally confirmed. Transcriptome analysis of GEP-NET-derived cells, perturbed with a library of 107 compounds, identified the HDAC class I inhibitor entinostat as a potent inhibitor of master regulator activity for 42% of metastatic GEP-NET patients, abrogating tumor growth in vivo. This approach may thus complement current efforts in precision oncology.

Abstract 5532: Functional role of Friend Leukemia Integration-1 (FLI1) in gastric carcinogenesis

Gastric adenocarcinoma (GC) is the 5th most common cancer worldwide but is the 3rd leading cause of cancer death. FLI1 (Friend leukemia integration-1) is an ETS family transcription factor that regulates genes involved in proliferation and differentiation. FLI1 is implicated in tumorigenesis, such as in Ewing’s sarcoma where a translocation creates an EWS-FLI1 oncogenic fusion protein. However, few studies have examined the role of FLI1 in carcinomas. In human breast cancer, overexpression of FLI1 led to inhibition of apoptosis, thereby promoting survival and malignant potential. In functional studies in a murine breast cancer model, however, downregulation of FLI1 increased malignant potential. In human GCs, we recently reported that FLI1 expression is inversely correlated with its promoter CpG methylation of the FLI1.

To determine if decreased expression occurs in GC epithelial cells or background non-epithelial cells, we analyzed 91 human GC tumors by immunohistochemistry (IHC) for FLI1 and compared them to normal gastric mucosa and intestinal metaplasia (IM) using an IHC composite scoring system accounting for intensity and percentage of epithelial cells expressing FLI1. We found that FLI1 is strongly expressed in normal gastric glandular epithelium and in IM, and that decreased expression was seen in most human GCs (P < 1x10-17 vs normal, P < 1x10-26 vs IM). These findings suggest that FLI1 acts as a tumor suppressor gene in GC. To test this hypothesis, we used an invasion assay and the human GC cell lines NUGC3 and SNU638, which have little to no FLI1 expression, respectively. Cultured GC cells were transduced to overexpress FLI1 or control, along with an eGFP reporter from an IRES (Lv203, Genecopoeia). After selection by puromycin, these GC cells were plated in serum-free media in the upper chamber on a Matrigel coated 8µm pore opaque membrane. Complete media with 10% fetal calf serum was plated in the lower chamber. Images were obtained of the lower membrane with an inverted fluorescent microscope and cellSens imaging software. Overexpression of FLI1 significantly decreased invasion by NUGC3 cells at 24 hours (P = 0.013) but not at 48 hours (P = 0.268) as compared to control. Overexpression of FLI1 significantly decreased invasion by SNU638 cells at both 24 and 48 hours (P = 0.027 and 0.012, respectively) as compared to control. Since NUGC3 cells have low FLI1 expression, we knocked down FLI1 by using a FLI1 shRNA lentiviral system with mCherry from an IRES as a reporter (LvRU6MP, Genecopoeia). Using the same invasion assay, knockdown of FLI1 trended towards a significant increase in invasion as compared to control at 48 hrs (P = 0.14), but not at 24 hrs (P = 0.73).

In summary, the combined observations in human GC tissue samples and the functional analyses in GC cells support a tumor suppressor role for FLI1 in human GC and also suggest that FLI1 and/or its target genes may be involved in regulatory mechanisms driving invasive properties of GC.

Citation Format: Armando Del Portillo, Elena V. Komissarova, Anne Koehne de Gonzalez, Aqiba Bokhari, Helen Remotti, Jorge Sepulveda, Antonia Sepulveda. Functional role of Friend Leukemia Integration-1 (FLI1) in gastric carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5532. doi:10.1158/1538-7445.AM2017-5532

Abstract 714: Human transcriptome alterations in pre-cancer and cancer epithelium identify candidate biomarkers of progression to pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most common cancers in the United States. The five-year survival rate for patients with PDAC remains dismal. Identification of biomarkers for early diagnosis of PDAC and pre-cancer pancreatic intraepithelial neoplasia (PanIN) lesions with risk of progression to PDAC is critically needed. We hypothesized that differentially expressed genes and regulatory pathways in PanIN and PDAC compared to normal duct epithelium (ND) may represent biomarkers of development of malignancy. We used Affymetrix Human Transcriptome Arrays 2.0 to establish gene expressionprofiles in ND, low-grade PanIN, and PDAC epithelium. Total RNA was isolated after laser capture microdissection (LCM) of frozen tissue sections and then used for producing hybridization-ready DNA. Hybridization quality control was performed with Expression Console 1.4 software and background corrected/normalized data were analyzed with Transcriptome Analysis Console (TAC) 3.1 and the ASSIGN algorithm. We tested RNA from 22 LCM samples (9 PDACs, 5 PanINs, and 8 ND), including 4 matched trios of ND, PanIN and PDAC from the same patients. Differential expression analysis with one-way between subject ANOVA revealed over 2000 genes differentially expressed in PDAC and PanIN vs. ND group (filter criteria up/down >2; ANOVA p<0.05). The most frequent alteration in PanIN compared to ND samples was upregulation of 433 genes and in PDAC compared to ND downregulation of 566. We found 60 (40 coding) upregulated genes and 750 downregulated genes (filter criteria up/down >1.5; ANOVA p<0.05) in both PanIN and PDAC vs. ND epithelium. Signaling pathway analysis of WikiPathways showed a number of significantly altered pathways in PDAC and PanIN compared to ND including the Gastric Cancer Network 1 with upregulated S100P in both PanIN and PDAC whereas other genes including CENPF, KIF20B,TPX2, and UBE2C were upregulated in PDAC only. Using the ASSIGN algorithm and the Kruskal-Willis test for analysis of difference in pathway activity, we found additional regulatory pathways with altered activity including Nuclear Receptor meta-pathway with reduced overall score in PDAC compared to PanIN and ND samples. In summary, over 400 genes were significantly up-regulated in pre-cancer PanIN lesions compared to normal duct epithelium, whereas gene down-regulation was the most frequent alteration in PDAC. Sixty genes, including 40 coding genes were up-regulated in both PDAC and PanIN. The altered pathways associated with the differentially expressed genes may represent an approach for integrated biomarker testing of neoplastic progression.

Citation Format: Elena V. Komissarova, Jorge Sepulveda, Sarawut Kongkarnka, Maryam Shirazi, Brynn Levy, Claudia Cujar, Antonia R. Sepulveda. Human transcriptome alterations in pre-cancer and cancer epithelium identify candidate biomarkers of progression to pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 714. doi:10.1158/1538-7445.AM2017-714

Role of the urokinase plasminogen activator receptor in mediating impaired efferocytosis of anti-SSA/Ro-bound apoptotic cardiocytes: Implications in the pathogenesis of congenital heart block

RATIONALE

Binding of maternal anti-Ro/La antibodies to cognate antigen expressed on apoptotic cardiocytes decreases clearance by healthy cardiocytes, which may contribute to the development of autoimmune associated congenital heart block and fatal cardiomyopathy.

OBJECTIVE

Given recent evidence implicating the urokinase plasminogen activator receptor (uPAR) as a "don't eat me" signal during efferocytosis, experiments addressed whether surface bound anti-Ro antibodies inhibit apoptotic cell removal via an effect on the expression/function of the urokinase-type plasminogen activator protease uPA/uPAR system.

METHODS AND RESULTS

As assessed by flow cytometry and confocal microscopy, uPAR colocalizes and interacts with Ro60 on the surface of apoptotic human fetal cardiocytes. Blocking of uPAR enhances phagocytosis of apoptotic cardiocytes by healthy cardiocytes and reverses the anti-Ro60-dependent impaired clearance of apoptotic cardiocytes. Binding of anti-Ro60 antibodies to apoptotic cardiocytes results in increased uPAR expression, as well as enhanced uPA activity. The binding of anti-Ro60 did not alter other surface molecules involved in cell recognition (calreticulin, CD31, or CD47).

CONCLUSIONS

These data suggest that increased uPAR expression and uPA activity induced by anti-Ro60 binding to the apoptotic fetal cardiocyte provide a molecular basis by which these antibodies inhibit efferocytosis and ultimately lead to scar of the fetal conduction system and working myocardium.

Evaluation of fetuses in a study of intravenous immunoglobulin as preventive therapy for congenital heart block: Results of a multicenter, prospective, open-label clinical trial

OBJECTIVE

The recurrence rate of anti-SSA/Ro-associated congenital heart block (CHB) is 17%. Sustained reversal of third-degree block has never been achieved. Based on potential reduction of maternal autoantibody titers as well as fetal inflammatory responses, intravenous immunoglobulin (IVIG) was evaluated as preventive therapy for CHB.

METHODS

A multicenter, prospective, open-label study based on Simon's 2-stage optimal design was initiated. Enrollment criteria included the presence of anti-SSA/Ro antibodies in the mother, birth of a previous child with CHB/neonatal lupus rash, current treatment with < or = 20 mg/day of prednisone, and <12 weeks pregnant. IVIG (400 mg/kg) was given every 3 weeks from week 12 to week 24 of gestation. The primary outcome was the development of second-degree or third-degree CHB.

RESULTS

Twenty mothers completed the IVIG protocol before the predetermined stopping rule of 3 cases of advanced CHB in the study was reached. CHB was detected at 19, 20, and 25 weeks; none of the cases occurred following the finding of an abnormal PR interval on fetal Doppler monitoring. One of these mothers had 2 previous children with CHB. One child without CHB developed a transient rash consistent with neonatal lupus. Sixteen children had no manifestations of neonatal lupus at birth. No significant changes in maternal titers of antibody to SSA/Ro, SSB/La, or Ro 52 kd were detected over the course of therapy or at delivery. There were no safety issues.

CONCLUSION

This study establishes the safety of IVIG and the feasibility of recruiting pregnant women who have previously had a child with CHB. However, IVIG at low doses consistent with replacement does not prevent the recurrence of CHB or reduce maternal antibody titers.

Arsenite induced poly(ADP-ribosyl)ation of tumor suppressor P53 in human skin keratinocytes as a possible mechanism for carcinogenesis associated with arsenic exposure

Arsenite is an environmental pollutant. Exposure to inorganic arsenic in drinking water is associated with elevated cancer risk, especially in skin. Arsenite alone does not cause skin cancer in animals, but arsenite can enhance the carcinogenicity of solar UV. Arsenite is not a significant mutagen at non-toxic concentrations, but it enhances the mutagenicity of other carcinogens. The tumor suppressor protein P53 and nuclear enzyme PARP-1 are both key players in DNA damage response. This laboratory demonstrated earlier that in cells treated with arsenite, the P53-dependent increase in p21(WAF1/CIP1) expression, normally a block to cell cycle progression after DNA damage, is deficient. Here we show that although long-term exposure of human keratinocytes (HaCaT) to a nontoxic concentration (0.1 microM) of arsenite decreases the level of global protein poly(ADP-ribosyl)ation, it increases poly(ADP-ribosyl)ation of P53 protein and PARP-1 protein abundance. We also demonstrate that exposure to 0.1 microM arsenite depresses the constitutive expression of p21 mRNA and P21 protein in HaCaT cells. Poly(ADP-ribosyl)ation of P53 is reported to block its activation, DNA binding and its functioning as a transcription factor. Our results suggest that arsenite's interference with activation of P53 via poly(ADP-ribosyl)ation may play a role in the comutagenic and cocarcinogenic effects of arsenite.

Gene expression levels in normal human lymphoblasts with variable sensitivities to arsenite: identification of GGT1 and NFKBIE expression levels as possible biomarkers of susceptibility

Drinking arsenic-contaminated water is associated with increased risk of neoplasias of the skin, lung, bladder and possibly other sites, as well as other diseases. Earlier, we showed that human lymphoblast lines from different normal unexposed donors showed variable sensitivities to the toxic effects of arsenite. In the present study, we used microarray analysis to compare the basal gene expression profiles between two arsenite-resistant (GM02707, GM00893) and two arsenite-sensitive lymphoblast lines (GM00546, GM00607). A number of genes were differentially expressed in arsenite-sensitive and arsenite-resistant cells. Among these, gamma-glutamyltranspeptidase 1 (GGT1) and NF kappa B inhibitor-epsilon (NFKBIE) showed higher expression levels in arsenite-resistant cells. RT-PCR analysis with gene-specific primers confirmed these results. Reduction of GGT1 expression level in arsenite-resistant lymphoblasts with GGT1-specific siRNA resulted in increased cell sensitivity to arsenite. In conclusion, we have demonstrated for the first time that expression levels of GGT1 and possibly NFKBIE might be useful as biomarkers of genetic susceptibility to arsenite. Expression microarrays can thus be exploited for identifying additional biomarkers of susceptibility to arsenite and to other toxicants.

Dead or dying: the importance of time in cytotoxicity assays using arsenite as an example

Arsenite is a toxicant and environmental pollutant associated with multisite neoplasias and other health effects. The wide range of doses used and the claims that some high doses are "not toxic" in some assays have confounded studies on its mechanism of action. The purpose of this study is to determine whether the treatment time and particularly the duration between treatment and assay are important factors in assessing arsenite toxicity. We compared three commonly used assays: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), neutral red (NR), and clonal survival, using human osteogenic sarcoma (HOS) cell line U-2OS. Results from the assays were well correlated only when the factor of time was taken into account. In both the MTT and NR assays, exposure to arsenite for 24 h induced much less toxicity than exposure for 48 or 72 h, which gave similar results. In contrast, results in clonal survival assays showed only a small difference between 24-h exposure and longer exposure times. Arsenite demonstrated delayed cytotoxicity, killing the cells even after its removal from the medium in NR assay. Apoptosis was assessed by TUNEL staining and caspase-3 activation. After treatment for 24 h with 0.1 and 1 microM arsenite, no apoptosis was seen. However, after an additional 24 h in arsenite-free medium, a small amount of apoptosis could be detected, and much more apoptosis was seen after 48 h. In contrast, 10 microM arsenite triggered rapid necrosis and failed to activate caspase 3 or cause TUNEL staining. We also confirmed previous reports that exposure to low concentrations of arsenite caused transient stimulation of cell growth. Our finding of delayed toxicity by arsenite suggests that to avoid underestimation of toxicity, the duration between treatment and assay should be taken into account in choosing appropriate doses for arsenite as well as for other toxicants that may show similar delayed toxicity. The NR and MTT assays should be performed only after an interval of at least 48 h after a 24-h exposure to arsenite.

Variability in sensitivity to arsenite does not correlate with arsenic accumulation rate in normal human lymphoblasts

Arsenic is a common environmental contaminant of our air, water and food, but not every individual who drinks arsenic-contaminated water shows clinical signs of toxicity. Large inter-individual variations are also found in arsenite-induced aneuploidy, chromosome aberrations and sister chromatid exchanges in peripheral blood lymphocytes from different human donors. Lymphoblasts are virally immortalized lymphocytes that retain most of the properties of lymphocytes. Individual lymphoblast cell lines retained their arsenite sensitivity after cryopreservation and subsequent revival. We measured the accumulation of 73[As]-arsenite into lymphoblast lines derived from 11 normal individuals. Arsenite accumulation rate varied 6.3 fold between the slowest and the fastest subjects. Assays in 14 lymphoblast lines showed variability to the toxic effects of arsenite, as measured by growth inhibition. Lymphoblast lines also vary with regard to their growth rates, but there is no relationship between growth rate and arsenite sensitivity. Surprisingly, we also found no correlation between arsenite accumulation rate and cellular sensitivity to growth inhibition, suggesting that the arsenite accumulation rate may not be the main determinant of cellular sensitivity to arsenic. We were also unable to detect evidence for a human homolog for the yeast arsenite efflux gene ACR3, using RT-PCR.

fau and its ubiquitin-like domain (FUBI) transforms human osteogenic sarcoma (HOS) cells to anchorage-independence

Arsenite is the most likely carcinogenic form of arsenic in the environment. Previously, expression cloning for cDNAs whose overexpression confers arsenite-resistance in Chinese hamster V79 cells identified two genes: fau and a novel gene, asr2. The fau gene encodes a ubiquitin-like protein (here called FUBI) fused to the ribosomal S30 protein. Since the expression of the fox sequence (antisense to fau) increased the tumorigenicity of a mouse sarcoma virus, it was proposed that fau might be a tumor suppressor gene. We intended to test its ability to block arsenite-induced transformation of human osteogenic sarcoma (HOS) cells to anchorage-independence. Instead, we found that overexpressing fau itself was able to transform HOS cells. When the two domains were expressed separately, only FUBI was transforming and only the S30 domain conferred arsenite resistance. An incidental finding was the transforming activity of the selectable marker, hyg. FUBI belongs to the ubiquitin-like protein group that is capable of forming conjugates to other proteins, although none have so far been identified. Alternatively, FUBI may act as a substitute or inhibitor of ubiquitin, to which it is most closely related, or to close ubiquitin-like relatives UCRP, FAT10, and/or Nedd8.

[Cathepsins L and B and their endogenous inhibitors in embryonal fibroblasts transformed by different genes]

Expression of cysteine proteinases, cathepsins L and B, and their inhibitors was studied out in three model systems of rat embryo fibroblasts, sequentially immortalized and transformed by different genes. In Model I rat embryo fibroblasts were immortalized with DNA of early region of simian adenovirus SA7 (clone REF-1) and then transformed by c-Ha-ras oncogene (REF-2EJ; malignant transformation). In Model II and III, the immortalized fibroblasts (clone IE5) were obtained by transfection with the polyoma virus LT gene and the clone IE5 used lost this gene; the malignant transformation was achieved by transfection with the E7 gene (clone trF8; Model II) and E6/E7 genes ¿clone A5E5(pC7-1); Model III]¿ of human papilloma virus types 16 and 18 respectively. In Model I, the increase in the total cathepsin L and B activity was correlated with the stages of transformation, at the same time, in Models II and III, this activity in immortalized IE5 fibroblasts was higher than at transformation stage. The activity of cathepsin L in lysates of transformed fibroblasts--REF-2EJ, significantly exceeded this activity both in transformed cells trF8 and A5E5(pC7-1)(6- and 10-fold, respectively). In cell cultures of Models I and II, the increases in secreted activity of cathepsins L and B were correlated with the stages of fibroblasts transformation, but in cultures of Model III, this activity at the stage of malignant transformation was lower than that the stage of immortalization. Therefore, the activities of cathepsins L and B were expressed to varying degrees at different stages of oncogenic transformation and the expression of their activities were dependent on type of transforming gene. It was established that changes in proteolytic potential were correlated with differences in the transforming phenotype of cell clones. An endogenous inhibitor(s) of cysteine proteinases was found in conditioned media of all type cell cultures. Expression and inhibitory properties of this inhibitor(s) were different at distinct stages of transformation.

Changes in surface relief of suspended cells are morphological signs of the initial stage of neoplastic transformation in fibroblastic monolayer cultures

The percentages of cells with different types of cell surface relief were determined in cell suspensions derived from monolayer cultures. Primary cultures of rat embryo fibroblasts (REF) and cell lines REF (LT) and REF-1, immortalized cells of which preserved normal phenotypic characteristics of the initial primary culture REF, as well as morphologically transformed tumorigenic lines REF (LT) ras and REF-2EJ were studied. In REF suspensions the cells with the blebbed type of surface relief were shown to be predominant as compared with those with microvillus relief whereas cell suspensions derived from both immortalized and fully transformed cultures display the reverse ratio of cells with those types of surface relief. Therefore, the pattern of cell surface relief in cell suspensions derived from fibroblastic monolayer cultures may serve as a morphological marker of the initial stage of neoplastic transformation-immortalization when typical morphological signs of cell transformation are not yet manifested in monolayer cultures.

[The effect of Ha-ras oncogene on cells immortalized by the gene for polyomavirus large T-antigen]

Activated human Ha-ras oncogene cloned on the plasmid pEJras6,6 was transfected into REF (LT) cells immortalized by the gene for large T-antigen of the polyoma virus. The cells were shown to become completely transformed (in the terms of morphology and tumorogeneity) only after three cycles of transfection with the plasmid pEJras6,6. The integrated sequences of the plasmid pEJras6,6 and the ras oncogene product p21Ha-ras were detected in cells only after their selection in the nude mice (in the cell culture REF (LT) ras X 3tu obtained from the tumor and directly in the tumor cells). Thus, after sequential transfections with a c-Ha-ras oncogene we developed cell cultures on the different stages of transformation process.

[Biochemical and functional changes during immunization of rats with angiotensin II]

Angiotensin-converting enzyme (ACE) activity in serum and some brain areas, level of angiotensin I in the blood and drinking behaviour during immunization of rats against conjugate of angiotensin II with bovine serum albumin (BSA) were studied. The results show that an increase in antibodies against angiotensin II was correlated with elevated ACE activity in serum. There was a distinct tendency towards elevated level of angiotensin I in the blood. After a 6 month's immunization ACE-activity was reduced twofold to threefold in midbrain and hypothalamus-thalamus. During immunization water-uptake was increased by 40-45%.

[Isolation of a stable cell line after transfection of rat embryo fibroblasts by the gene of the polyomavirus large T antigen]

A stable cell line REF(LT) was established upon transfection of DNA plasmid containing a large T gene of polyoma virus. REF(LT) cells grow in a monolayer, their growth depends on the underlayer, they are non-carcinogenic. The dependence of cellular growth on serum factors is decreased.

[Expression of virus-specific RNA in cells of mice infected with Mazurenko and Rauscher viruses]

Organs of mice with leukemia induced by Rauscher and Mazurenko viruses contain different amounts of virus-specific RNA. In Mazurenko virus-induced leukemia, virus-specific RNA content reached the maximum in the thymus and lymph nodes. Hybridization level of RLV 3H DNA transcript with RNA from mouse cells with RLV-induced leukemia amounted to 90% while in cells of mice with Mazurenko virus-induced leukemia it did not exceed 60%.